Vulcanized elastomeric compositions frequently contain antioxidants and antiozonants for the purpose of enhancing the aging properties of the composition. The most commonly employed antioxidants and antiozonants are classified as staining antidegradants because they are in physical admixture with the polymer and can migrate to a surface of an article and discolor the article. Some of these straining antidegradants can even cause contact staining of a second article that comes into contact with the article containing the staining antidegradants. While the new elastomeric composition has particular utility in tires, it could be used as an outer layer of other elastomeric articles such as belts, hoses and roofing.
It has been a common practice in the tire art that when a white stripe, or white lettering, is to be placed on a tire sidewall a barrier strip of non-staining material is placed between the white rubber and the black rubber which contains staining antidegradants. If a barrier strip is not employed the surface of the white rubber will be discolored by the staining antidegradants that migrate to the surface. This new composition has particular utility when used with liquid coating materials such as taught in U.S. Pat. No. 4,535,114 and U.S. Pat. No. 4,668,728. These liquid coating materials are used for painting indicium on a sulfur cured rubber article, and the indicium would be discolored by the staining antidegradants contained in the prior art compositions. That problem of staining the indicia can be overcome with the present invention.
Another disadvantage in relying upon staining antidegradants for antioxidant and antiozonant properties in a tire, especially a truck tire or aircraft tire, is that over an extended period of time (covered by several retread lives of the tire) substantially all of the staining antidegradants in a sidewall of the tire will have migrated to the surface and be abraded or washed away. In such an instance an otherwise retreadable tire carcass will be left vulnerable to deterioration by oxygen and ozone.
There is provided in accordance with one aspect of the invention a non-staining elastomeric composition which prior to vulcanization comprises by weight 25 to 90 parts diene rubber, 10 to 75 parts crosslinkable EPDM, 0.5 to 10 phr of a polymeric antidegradant, and a vulcanizing amount of a cure package, said composition being substantially free of staining antidegradants.
There is provided in accordance with a second aspect of the invention an elastomeric article having an outer layer comprising a non-staining elastomeric composition which prior to vulcanization comprises diene rubber, crosslinkable EPDM and a polymeric antidegradant.
There is provided in accordance with a third aspect of the invention a tire comprising a sidewall portion having at least an axially outer layer comprising a non-staining vulcanized elastomeric composition which prior to vulcanization comprises by weight 25 to 90 parts diene rubber, 10 to 75 parts crosslinkable EPDM, 0.5 to 10 phr of a polymeric antidegradant, and a vulcanizing amount of a cure package, said composition being substantially free of staining antidegradants.
There is provided in accordance with a fourth aspect of the invention a tire comprising a sidewall portion having an axially outer layer comprising a non-staining vulcanized elastomeric composition which is substantially free of staining antidegradants and which prior to vulcanization comprises by weight:
(a) 60 to 80 parts of a blend of (i) 35 to 45 parts natural rubber and (ii) 25 to 35 parts polybutadiene rubber;
(b) 25 to 35 parts of a chlorothio-sulfonamide-modified EPDM which is crosslinkable with said blend described in (a) during vulcanization;
(c) 1.0 to 4 parts of a polymeric antidegradant which consists essentially of segmeric units derived from N-(4-anilinophenyl)methacrylamide;
(d) 40 to 60 parts carbon black;
(e) 0.1 to 2 parts stearic acid;
(f) 5 to 15 parts processing oils and/or tackifiers; and
(g) a vulcanizing amount of a sulfur cure package.